Re: [ferret_users] how does @DIN work on the pressure coordinate

[Karl Smith - NOAA Affiliate <karl.smith@xxxxxxxx>]

Hi Xiaoyu,

`@DIN` is just a numerical integral - multiply the cell width (which in your case is a difference in pressure rather than distance in meters) by the data value in that cell and sum these up. As always, be conscious of the units of the computed value. There is the special case if you are integrating over both longitude and latitude (Ferret computes an area value of the cell assuming a spherical earth), but you are not doing that here.

If your pressure axis is marked as a depth-type axis then positive is down. Use a `show grid` for the variable, and if axis is positive-down, there will be a minus sign after the number of points; for example (from levitus_climatology):

ZAXLEVITR DEPTH (m) 20 i- 0 5000 full

You can explicitly specify the range for the integration to make it clear what region you are integrating over:

SALT[Z=0:5000@DIN]

Karl

On Wed, Sep 4, 2019 at 10:57 AM Xiaoyu Bai <xbai1@xxxxxxxx> wrote:

Dear ferreters,

I am reading the instruction of@DIN from../../documentation/users-guide/variables-xpressions/XPRESSIONS.html. I noticed that we can use@DIN for the Z-axis for variables like salinity. I am wondering how does@DIN work for the pressure coordinate? How

--

Karl M. Smith, Ph.D.
JISAO Univ. Wash. and PMEL NOAA
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